Meet the Tiniest Wing-Propelled Diver

Most wing-propelled diving birds are fairly large, ocean-going fellows. Not so for the smallest species to adapt this strategy. Cinclidae are a very special group of songbirds that hunt underwater for insect prey in freshwater streams. These marvelous little birds are capable of both “walking” along the bottom by gripping the substrate and of propelling themselves through the water column with their wings. Today, five species can be found. As a group these species have spread throughout much of the world including North America, Europe, Asia and Africa.

American Dipper (Cinclus mexicanus) on Kodiak Island. Photo from U.S. Fish and Wildlife Service.

Dippers look rather unassuming when on land, and it would be easy to mistake them for catbirds or other garden variety songbirds at a glance. However, detailed studies have revealed many evolutionary novelties associated with more efficient waterproofing of the feathers, modified wing musculature to assist in the underwater “flight” stroke, and physiological properties of blood haemoglobin that make them very efficient at employing their unique feeding strategy. DNA studies indicate that the closest relatives of the dippers are thrushes and Old World flycatchers, but these groups show no particular affinities for water.

Our team is studying the dipper to learn what it can tell us about the earliest stages of wing-propelled diving. Since dippers make only shallow dives, are very small, and spend much time on land, they may provide clues about which evolutionary changes happen first during the transitions from a non-diving, volant bird body plan to a flightless diving bird body plan (like that of penguins).

March of the Fossil Penguins

written by Dr. Daniel Ksepka

This blog details fossil discoveries and research on the fascinating Sphenisciformes. The aim is to introduce the cast of fossil species (50 and counting), explore the evolutionary history of penguin bones, feathers and ecology, and explain how scientists learn about life in the past.